1. Field of the Invention
The present invention relates to an aperture regulating apparatus for changing the aperture size in accordance with the focal length of a taking lens.
2. Background Arts
A low-priced shutter mechanism (a program shutter) which is also used as an aperture stop with a moving-magnet motor is generally known. The motor opens and closes a shutter blade, by means of making a rotor of a permanent magnet reciprocate within a range of a predetermined angle, in response to a current direction flowing in a coil. The moving-magnet motor is inexpensive as compared to a pulse motor, but it cannot control the aperture size precisely in accordance with an exposure value. In order to realize the proper exposure value, the shutter mechanism is equipped with a regulation device for regulating a rotational range of the shutter blade so as to control the exposure time.
If a zoom lens is used with the shutter mechanism which controls the exposure time in accordance with the exposure value, brightness of the zoom lens differs between a wide-angle side and a telephoto side. Hence, it is necessary to make the aperture size in the wide-angle side smaller than that in the telephoto side. Furthermore, the small aperture size is preferable in the wide-angle side, for the purpose of reducing blurriness of the edge of an image frame caused by spherical aberration of the lens. From this point of view, U.S. Pat. No. 6,222,684 (corresponding to Japanese Patent Laid-Open Publication No. 2000-235209) and Japanese Patent Laid-Open Publication No. 2000-352657 disclosed aperture regulating apparatuses for a zoom lens which changes a maximum aperture size formed by shutter blades in accordance with the focal length of the zoom lens.
The aperture regulating apparatus according to U.S. Pat. No. 6,222,684 has a moving barrel for holding a lens group and a program shutter doubling as an aperture stop, and a rotation barrel held on an outer periphery of the moving barrel. The rotation barrel moves in an optical axis direction in response to magnifying. One end portion of a driving lever for operating the shutter blades protrudes outside from the program shutter. A cam inclined to the optical axis direction is provided inside the rotation barrel. Upon zooming within a predetermined range on a wide-angle side, the end portion of the driving lever is engaged with the cam to regulate a rotational range of the driving lever. Thus, the aperture size is regulated in the predetermined zooming range in accordance with the focal length of the taking lens.
The aperture regulating apparatus according to Japanese Patent Laid-Open Publication No. 2000-352657 has a moving barrel for holding a lens group and a program shutter, and a straight guide frame for preventing rotation of the moving barrel. A cam is formed in the straight guide frame. In response to magnifying, the straight guide frame and the moving barrel relatively moves in an optical axis direction. Such relative movement causes the cam to push the regulation lever for regulating the movement of the shutter blades, so that the aperture size is regulated.
In the aperture regulating apparatuses described above, however, movement of the rotation barrel or the straight guide frame in the optical axis direction with zooming changes an overlap area between the moving barrel and the rotation barrel, or between the moving barrel and the straight guide frame. It is possible to engage the part of the driving lever or the regulation lever with the cam in the wide-angle side because the overlap area is wide therein, but it becomes impossible in the telephoto side because the overlap area is narrow therein. To realize the engagement in the telephoto side, the rotation barrel or the straight guide frame may be extended to the optical axis direction. In this case, however, length of a lens barrel becomes long along the optical axis direction. Such aperture regulating apparatus, if assembled in a camera containing the lens barrel inside the camera body, causes an increase in thickness of the camera body, which adversely affects miniaturization of the camera.
An object of the present invention is to provide an aperture regulating apparatus which can regulate the aperture size in the whole zooming range.
Another object of the present invention is to provide an aperture regulating apparatus with compact structure.
To achieve the above objects, an aperture regulating apparatus according to the present invention comprises a moving barrel that moves straight in an optical axis direction, a rotation barrel movably held by the moving barrel, a cam member fitted on an outer surface of the moving barrel, a shutter unit contained inside the moving barrel, and a regulation lever engaged with the cam member. When the moving barrel moves in the optical axis direction, the rotation barrel moves in the optical axis direction with the moving barrel and rotates due to the straight movement of the moving barrel. The cam member moves straight in the optical axis direction relative to the moving barrel in accordance with the rotation of the rotation barrel. The shutter unit has shutter blades. The regulation lever is displaced in accordance with a movement of the cam member to regulate the range of movement of the shutter blades. An aperture size is changed by the regulation.
A first cam groove is formed in an inner surface of the rotation barrel, and a projection fitted into the first cam groove is provided on the cam member. When the rotation barrel rotates, the first cam groove and the projection move the cam member in the optical axis direction.
Plural cam steps are formed in the cam member. A position of the regulation lever is regulated within plural steps depending on a position of the cam member against the moving barrel.
The aperture regulating apparatus further comprises at least one second cam groove formed in an inner surface of the rotation barrel, at least one guide opening formed in a periphery of the moving barrel along the optical axis direction, and at least one cam follower provided in the shutter unit. The cam follower is fitted into the second cam groove through the guide opening, so that the shutter unit moves in the optical axis direction when the rotation barrel rotates.
The first cam groove and the second cam groove may be connected with each other in the inner surface of the rotation barrel. Three of the second cam grooves may be formed in rotational symmetrical positions.
The aperture size determined in magnifying is kept constant during the focusing operation of a taking lens optical system.
The taking lens optical system comprises a lens group moving in the optical axis direction together with the shutter unit. The shutter unit moves in the optical axis direction while keeping a distance from the cam member during the focusing operation of the taking lens optical system, so that the position of the lens group is changed in the taking lens optical system.
The regulation lever is movably held inside the shutter unit. A first end of the regulation lever protruding outside from the shutter unit is engaged with the cam member. The regulation lever rotates within a vertical plane to the optical axis direction when the cam member moves in the optical axis direction.
A second end of the regulation lever gets in range of movement of the shutter blade. The position of the second end is changed in accordance with an amount of rotation of the regulation lever to control an amount of rotation of the shutter blades.